JPH06321678A - Crucible for pulling up crystal - Google Patents

Abstract

PURPOSE:To improve a yield and efficiency by setting the radius of curvature of the base of the crucible for pulling up a silicon crystal and the radius of curvature in the boundary part between the base and flank as prescribed calculation values. CONSTITUTION:The radius R1 of curvature of the base of the quartz crucible for pulling up the silicon crystal by a CZ method is set on the basis of the value of equation I {ya is the value of y (coordinate) satisfying F(y)=0 and the numerical value of equation III (V is the volume of the residual amt. of melt); (a) is the numerical value of equation VI}. The crucible is then produced by setting the radius R2 of curvature in the boundary part between the base of the crucible and the flank thereof by the calculation numerical value of equation II {(b) is the numerical value of equation IV; (c) is the numerical value of equation V; 2r is the outside diameter of an evaporation preventive member partially covering the free surface of the melt; 2R0 is the inside diameter of the crucible}. The crucible for pulling up the silicon crystal which operates so as to suppress the evaporation of oxygen by doping and to control the oxygen concn. in the crystal is thus produced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is intended to obtain a target oxygen concentration by preventing evaporation of oxygen due to the action of a dopant and lowering the oxygen concentration of the crystal in the silicon crystal growth by the CZ method. A crucible for pulling up a crystal.

[0002]

2. Description of the Related Art In the growth of silicon crystals by the CZ method,
When a large amount of antimony is doped, the evaporation of oxygen from the melt is promoted, and the oxygen concentration in the melt becomes low, so that there is a problem that the oxygen concentration in the grown silicon crystal also becomes low. Therefore, in order to prevent the decrease of the oxygen concentration by controlling the evaporation of oxygen from the melt, a method or apparatus for installing a member made of quartz or boron nitride (hereinafter referred to as an evaporation preventing member) on the melt surface part is available. Proposed (JP-A-57-17909)
No. 9, JP-B-60-28798, JP-A-61.
No. 146788, Japanese Unexamined Patent Publication No. 63-129091, Japanese Unexamined Patent Publication No. 1-212292, etc.).

[0003]

In the pulling of silicon crystal by the CZ method, oxygen is eluted from the quartz crucible.
A part of oxygen eluted from the quartz crucible is taken into the crystal, and most of the rest is evaporated from the free surface of the melt. FIG. 3 schematically shows the movement of oxygen. When a large amount of antimony is doped, there is a problem that the oxygen concentration in the grown silicon crystal becomes low as compared with the case where it is not doped. It is known that the cause of this is that when a large amount of antimony is doped, the evaporation of oxygen from the melt surface is promoted and the oxygen concentration in the melt becomes low (Z. Liu and T. . Carlb
erg, J .; Electrochem. Soc. , Vo
l. 138, No. 5, May 1991, p148
8).

Therefore, in the case where a large amount of antimony is doped, in order to suppress the reduction of the oxygen concentration in the crystal, it is sufficient to suppress the evaporation of oxygen from the melt surface and increase the oxygen concentration in the melt. Therefore, as shown in FIG. 4, conventionally, a method and an apparatus for installing the evaporation preventing member 4 on the surface portion of the melt 2 have been proposed. In FIG. 4, 1
Is a crucible, 3 is a crystal, and 5 is a holding arm. But,
These conventional techniques have the following problems.

As described above, the following points should be noted when installing the evaporation preventing member on the melt surface. (1) It is necessary to install the evaporation preventing material at a distance from the crystal growth interface so as not to hinder the crystal growth. (2) It is necessary to install the evaporation prevention member at a distance from the wall of the quartz crucible so that the quartz crucible and the evaporation prevention material do not come into contact with each other.

The above two points are as follows:
If the size of the evaporation prevention member is properly selected, there will be no particular problem. However, as crystal growth progresses and the amount of melt decreases, contact with the quartz crucible becomes a problem. That is, since a quartz crucible that is usually used has a spherical bottom portion, the distance to the crucible wall on the melt free surface becomes shorter as the amount of melt decreases. Then, when the evaporation preventing member and the quartz crucible come into contact with each other, the melt becomes wavy due to the influence, and the crystal becomes polycrystal. There is also a risk that the jig holding the evaporation preventing member will be damaged.

Therefore, when pulling up using the evaporation preventing member, it is an essential condition to finish pulling up before the evaporation preventing member and the quartz crucible come into contact with each other. But,
Conventionally used quartz crucibles have a spherical bottom, and the radius of curvature of the spherical surface has an inappropriate value.Therefore, pull up before the evaporation prevention member and quartz crucible contact. When finished, there was a problem that a large amount of melt remained without being pulled up. as a result,
The yield was poor when the pulling up using the evaporation prevention member was performed.

The present invention has been made in order to solve the above problems, and an object thereof is to suppress evaporation of oxygen from the melt surface by using an evaporation preventing member to obtain the target oxygen. It is to provide a crucible whose shape is determined according to the maximum outer diameter of the evaporation preventing member used when pulling up a crystal having a concentration.

[0009]

In order to achieve the above object, the present invention creates a model formula for calculating the radius of curvature of the bottom of the crucible. In this model formula, the target values of the inner diameter of the crucible to be used, the outermost diameter of the evaporation preventing member, and the amount of melt remaining in the crucible after completion of pulling (hereinafter referred to as the amount of remaining hot water) are used as inputs. The meaning of the target value of the amount of remaining hot water is as follows.

Even in the normal pulling up without using the evaporation preventing member, it is difficult to pull up all the melt in the crucible, and the pulling up is always completed with the melt remaining. At this time, the pulling-up condition is set so that the pulling-up ends with a predetermined remaining hot water amount as a target. Similarly, when pulling up using the evaporation prevention member, pulling up conditions are set so that the pulling up is completed with a predetermined residual hot water amount as a target. The above-mentioned target value of the amount of remaining hot water is this value.

The present invention is used in the CZ method in which the free surface of the melt is partially covered to suppress the evaporation of oxygen due to doping and to control the oxygen concentration in the crystal.
_1. Applied to a silicon crystal pulling crucible having a radius of curvature R ₂ at the boundary between the bottom surface and the side surface, the following technical means were adopted. That is, the crystal pulling crucible is characterized in that the radii of curvature R ₁ and R ₂ are set on the basis of the values calculated by the following formula.

R ₁ = (ya ² + r ² ) / 2ya R ₂ = {-b- (b ² -4c) ^1/2 } / 2 where ya is the y (coordinate) satisfying F (y) = 0. a ^{value, F (y) = y 3} + 3r 2 y-6V / π b = {2 (R 1 -R 0 -a 2 R 0)} / a 2 c = (a 2 R 0 2 -R 1 2 + R ₀ ² ) / a ² a = (R ₁ −ya) / r, where 2r is the outer diameter of the member that partially covers the free surface of the melt, V is the volume of the amount of residual hot water, 2R ₀ is the inner diameter of the crucible.

[0013]

In a quartz crucible normally used in pulling a silicon crystal by the CZ method, the bottom portion has a spherical shape as shown in FIG. The spherical surface has a radius of curvature of two steps so that the boundary with the side wall is gentle. FIG. 1 schematically shows the shape of the quartz crucible of the present invention. The radius of curvature of the bottom portion is R1, the radius of curvature R2 of the boundary portion between the bottom portion and the side surface, and the outer diameter of the evaporation prevention member is 2r.
And At the end of pulling up, assuming that the evaporation prevention member is in contact with the portion of the crucible bottom where the radius of curvature changes from R1 to R2, the radius of curvature R1 is calculated using the outer diameter of the evaporation prevention member and the target value of the amount of remaining hot water. , R2 will be described below.

In FIG. 1, the coordinates of the portion where the evaporation preventing member and the quartz crucible contact each other are (r, ya), and the volume of the residual hot water is V.
Then, V can be expressed by the following equation.

[0015]

[Equation 1]

Since the triangle ABC is a right triangle, r ² + (R1-ya) ² = R1 ² R1 ² -2R1ya + ya ² + r ² = R1 ² ∴R1 = (ya ² + r ² ) / 2ya ( 2) Substituting equation (2) into equation (1),

[0017]

[Equation 2]

∴ya ³ + 3r ² ya-6V / π = 0 (3) Here, it is defined as F (y) = y ³ + 3r ² y-6V / π. Therefore, if ya satisfying the equation (3) is obtained by numerical calculation and is substituted into the equation (2), the radius of curvature R1 of the crucible bottom is R1.
Is required. Next, let the center of the circle of radius R2 be E (x1,
y1), assuming that the inner diameter of the crucible is 2R0, x1 = R0-R2 (4) y1 = R1-{(R1-R2) ² -x1 ² } ^1/2 (5) The triangle ADE and the triangle EFC are Because they are similar

[0019]

[Equation 3]

[0020] ∴ya = R1-r (R1- y1) / x1 ...... (6) is substituted into equation (6) to (5), ya = R1-r {R1 -R2) 2 -xl 2} 1 ^{/ 2} / x1

[0021]

[Equation 4]

Here, when a = (R1-ya) / r is set, a ² xl ² = (R1-R2) ² -xl ² (7) When the expression (4) is substituted into the expression (7), , A ² (R0-R2) ² = (R1-R2) ^2- (R0-R
2) ² ∴a ² R2 ² +2 (R1-R0-a ² R0) R2 + a ²
RO ² −R1 ² + R0 ² = 0 where:

[0023]

[Equation 5]

Putting it another way, R2 ² + bR2 + c = 0

[0025]

[Equation 6]

From the equation (8), two R2s are obtained, which means that there are two types of cylinders having a radius R0 and two spheres inscribed in a spherical surface having a radius R1. As the radius of curvature of the crucible bottom, the smaller value of R2 obtained by the equation (8) may be adopted. Therefore, if the inner diameter of the crucible to be used, the outer diameter of the evaporation preventing member, and the target amount of remaining hot water are given, the curvature radii R1 and R2 of the crucible bottom satisfying those conditions can be obtained.

Since the present invention can prevent the evaporation preventing member and the crucible from coming into contact with each other before the target amount of remaining hot water is reached, the amount of remaining hot water can be reduced even when the evaporation preventing member is pulled up. It is possible to achieve the same amount as the pulling without using, and to exert an excellent effect in increasing the efficiency of pulling a high quality crystal.

[0028]

EXAMPLE An example in which the present invention is applied to the pulling up of a 6-inch diameter antimony-doped ingot will be described. The inner diameter of the crucible used is 2R0 = -400mm, the outer diameter of the evaporation prevention member is 2r = 360mm, and the target value of the amount of remaining hot water is 3k.
g (hence the volume V = 3000 g / 2.33 × 10 ⁻³ g /
mm ³ , 2.33 × 10 ⁻³ : specific gravity of silicon).
The target value for the amount of remaining hot water was set to be the same as the target value for normal pulling without using the evaporation prevention member.

Using these values, first, according to the equation (3),
I asked for ya. FIG. 2 shows F (y) obtained from the equation (3). Since y is ya when F (y) = 0, it is set to ya = 25 mm from FIG. Next, ya = 25mm
Is substituted into the equation (2), R1 = 660.5 mm is obtained.

Further, by substituting these values into the equation (8), R
Calculating 2, gives R2 = 27.5, 298.6 mm. As described in the section of the concrete constitution of the invention, R2
Since it is necessary to adopt the smaller value as
= 27.5 mm. The radius of curvature R1a, R2a at the bottom of the crucible actually used may be a positive value close to R1, R2 with R1 and R2 as references. In this embodiment, R1a = 661 mm, R2a = 27 m
m.

Therefore, a crucible having the above dimensions was prepared and pulled up. On the other hand, in a normal crucible currently marketed for pulling a silicon single crystal, when the crucible inner diameter is 400 mm, R1a = 450 mm, R2a =
90 mm is the standard size. So, for comparison,
Pulling up using a commercially available crucible was also performed.

In each case, 45 kg of raw material polysilicon was charged and an evaporation preventing member having an outer diameter of 360 mm was installed. As a result, in the pulling up using the crucible of the present invention, the pulling up could be completed with the residual hot water amount of 3.1 kg. On the other hand, in pulling up using a commercially available crucible, when the amount of remaining hot water reached 6 kg, the crucible and the evaporation preventing member contacted and the pulling up was stopped.

As described above, according to the present invention, even when pulling up using the evaporation preventing member, pulling up can be completed with the same amount of residual hot water as in normal pulling up.

[0034]

As described above, according to the present invention, even when pulling up using the evaporation preventing member, pulling up can be completed with the same amount of remaining hot water as in normal pulling up. As a result, the yield of pulling using the evaporation preventing member was improved to the same value as that when the evaporation preventing member was not used, and the excellent effect of increasing the efficiency of pulling a good crystal could be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory diagram for analyzing a radius of curvature of a crucible of the present invention.

FIG. 2 is a relationship graph between y and F (y) in the vicinity of F (y) = 0.

FIG. 3 is an explanatory diagram showing movement of oxygen during pulling up silicon.

FIG. 4 is an explanatory view of a pulling device using an oxygen evaporation preventing member.

FIG. 5 is an explanatory view showing the shape of a commercially available quartz crucible.

[Explanation of symbols]

 1 crucible 2 melt 3 crystal 4 member 5 holding arm R0 1/2 of inner diameter of crucible R1 radius of curvature at bottom of crucible R2 radius of curvature at boundary between bottom and side of crucible r 1/2 of outer diameter of evaporation prevention member

Claims (1)

[Claims] 1. Used in the CZ method for partially covering the free surface of a melt to suppress the evaporation of oxygen due to doping and controlling the oxygen concentration in crystals, the radius of curvature R _{1 of} the bottom surface, and the bottom surface and the side surface. A crucible for pulling up a silicon crystal having a radius of curvature R ₂ at a boundary portion, wherein the curvature radii R ₁ and R ₂ are set on the basis of a value calculated by the following formula. R ₁ = (ya ² + r ² ) / 2ya R ₂ = {-b- (b ² -4c) ^1/2 } / 2 where ya is the value of y (coordinates) satisfying F (y) = 0, ^{F (y) = y 3 +} 3r 2 y-6V / π b = {2 (R 1 -R 0 -a 2 R 0)} / a 2 c = (a 2 R 0 2 -R 1 2 + R 0 2) / A ² a = (R ₁ −ya) / r, where 2r is the outer diameter of the member that partially covers the free surface of the melt, V is the volume of the amount of residual hot water, 2R ₀ is the inner diameter of the crucible.